The availability of mutants which demonstrate behavioral alterations in Paramecium provides a handy system to study the biochemical aspects of membrane dynamics. The locomotory behavior of this ciliate is related to the properties of the excitable surface membrane. Genetic and electrophysiological analyses of the mutant "pawn" have been reported. The surface membrane of this mutant has been altered in only one detectable aspect; the inability to demonstrate excitability in response to stimuli. The consequence of excitability in wild type cells is the increase in membrane conductance to Ca ion following depolarization. The increased conductance allows the cation to enter the cell by diffusion along its electrochemical gradient. The resulting increase in intracellular Ca ion is correlated with ciliary reversal. Hence, the failure of "pawn" to exhibit ciliary reversal and backward swimming is directly related to the inexcitability of the surface membrane. The project proposed here is an attempt to identify biochemical correlates with the specific change in the physiology of this membrane. The feasibility of adding biochemical data to the presently available electrophysiological and genetic data is promising. The probabilities are good that these ciliates can be grown in large quantities under stringent conditions and membrane preparations of high purity can be obtained. The expertise in biochemical analyses, particularly of the lipids, are available in the laboratory and under consultation from other laboratories. The system has great potentials as a model for understanding excitable membranes such as those found in nerves and muscles.